Can I use Source Filmmaker models in Blender?
It took me a while to figure this out but I finally figured out how to do it.

First you need to download WineBottler (https://winebottler.kronenberg.org/) This program allows you to run Windows applications on Mac. 

Once WineBottler has been installed, download Noesis (http://www.richwhitehouse.com/index.php?content=inc_res.php&amp;rescat=File%20List) 
-I'm not sure if the version mattwers, but I download v4202.
Once you install Noesis open the noesis.exe file in the Noesis folder. A Wine window will open up, press go. Now the software will open up and all you need to do is locate the file for the model you downloaded and click file>export. Then you can convert the model to a format importable to Blender (like .dae or .fbx)

Also, if you are going to use models from the Steam workshop you can only download them via: http://steamworkshopdownloader.com/